Research On The Reconstruction Algorithms In Corneal Topography System And Their Applications

With the development of corneal surgery, corneal topography system has become an indispensable equipment in ophthalmic diagnosis. Placido disc which has the advantage of high precision and low cost is widely used in corneal check. And it is simple structural, low sensitivity to noise, more suitable for clinical use compared with other method. The paper laid emphasis on the research and application of reconstruction algorithm of Placido disk. A reconstruction algorithm based on the precisely location of corneal vertex has been proposed. By the application of the method we have developed the corneal topography software system. The main work of this paper are as follows:1. The corneal structure and physiological characteristics have been researched, and we introduced the history and present situation of corneal topography.2. The key technology of the system has been deeply researched. This paper introduces the system principle and hardware structure. We expounded the auto center and auto focus method in image acquisition in detail. Further more, we studied the methods of image processing, including image preprocessing, the center location and the extraction of feature points.3. We conscientiously analyzed traditional methods of corneal reconstruction, and the algorithm which based on the precisely location of corneal vertex was proposed. By the reference to the formula of single spherical lens, we can solve the problem of the relationship between the 1st reflection point and the corneal vertex. By doing so, the corneal vertex can be precisely located. The position of reflection points and corneal Diopter have been calculated by using the algorithm. Finally by establishing Diopter data field grid and linear color-coding table, we built the pseudo color map.4. We calculated the local parameters and the global parameters of corneal by using the algorithm in this paper. Local parameter including Diopter information and elevation information; global parameters include simulated Keratometer, surface asymmetric index and surface regularity index. We discussed the characteristic of local parameter of and their applicable occasions, and analyzed the significance of global parameters.5. The precision and stability of the algorithm was verified by capture the image of some standard steel sphere. The result showed that the algorithm is more accurate than traditional methods and can be applied to larger Diopter range, which is satisfy for clinical use.